The existing methodology for platelet counting has not been entirely dependable. Automated versions of these methods have relied on chemistries which lead to platelet counts which are falsely elevated.
In typical platelet counting procedures, a material is added to a whole blood sample to lyse the red blood cells. Unfortunately, lysing procedures used up to the present time have had deleterious side-effects: material from the platelet themselves are extracted, some white blood cells are fragmented, and in some cases, protein precipitates are formed. When any of these occurrences takes place, the recorded platelet count is falsely elevated.
Regarding differential white blood cell count techniques presently available, it has not been possible to obtain leukocytes free from red blood cells by lysing without doing some concomitant damage to the leukocytes. Therefore, adequate differentiation of leukocytes as described in U.S. Pat. No. 3,741,875 is not possible unless the cells are stained by cytochemical reaction.